The present invention concerns coolant and antifreeze compositions for use in the cooling systems of internal combustion engines. More particularly, the invention relates to additive compositions for improving the properties of antifreeze and coolant compositions.
In general, water-based cooling compositions are employed for cooling internal engines. The coolants contain alcohols and glycols as antifreeze agents. The compositions can be oxidized to acidic materials by contact with air at operating temperatures and corrode metal parts of the cooling system of the engine.
It is a known practice to include in antifreeze and coolant composition additives that are designed to inhibit corrosion of the various metals which are present in cooling systems. These additives are known as corrosion inhibitors or metal deactivators. Antioxidants are added to prevent oxidation of the composition and subsequent sludge formation.
Prior art antifreeze and coolant compositions have contained as corrosion inhibitors aromatic carboxylic acid, e.g. benzoic acid as disclosed in U.S. Pat. No. 5,085,793. Another antifreeze and coolant composition is disclosed in U.S. Pat. No. 4,219,433 which teaches corrosion inhibition by addition of benzoic acid, trialkanolamine, organic phosphate and benzothiazole or benzotriazole compounds.
Another application for corrosion inhibitors is their use in lubricating compositions. U.S. Pat. No. 3,966,623 teaches a synergistic corrosion inhibiting composition of 2,5-bis-(alkenyldithio)-1,3,4-thiadiazole and aliphatic amine salt of 2-mercaptobenzothiazole. U.S. Pat. No. 4,233,176 discloses a silver corrosion inhibitor composition based on lubricating oil and containing monobasic acid, aminoalkylalkanolamine, an organic amine compound and benzoic acid. British Pat. No. 1,566,830 discloses primary and secondary amine derivatives of 2,5-dimercapto-1,3,4-thiadiazole said to possess antiwear and corrosion properties.
The above cited prior art shows the use of thiadiazole compounds as corrosion inhibitors for lubricating oils. The present invention is not directed to imparting anticorrosion properties to lubricating compositions affording corrosion protection to the lubricated parts of the engine. The invention is directed to cooling and antifreeze compositions and to the corrosion protection of cooling systems coming into contact with said compositions.
Surprisingly, it has been discovered that particular compositions based on monoallylamine derivative of 2,5-dimercapto-1,3,4-thiadiazole and of benzoic acid display improved metal corrosion inhibiting effect when incorporated into cooling or antifreeze compositions. In addition, the compositions stabilize the antifreeze compositions against oxidative degradation and further enhance the properties of said compositions.